Cost-of-illness studies: a guide to critical evaluation.

Cost-of-illness (COI) studies aim to assess the economic burden of health problems on the population overall, and they are conducted for an ever widening range of health conditions and geographical settings. While they attract much interest from public health advocates and healthcare policy makers, inconsistencies in the way in which they are conducted and a lack of transparency in reporting have made interpretation difficult, and have ostensibly limited their usefulness. Yet there is surprisingly little in the literature to assist the non-expert in critically evaluating these studies. This article aims to provide non-expert readers with a straightforward guide to understanding and evaluating traditional COI studies. The intention is to equip a general audience with an understanding of the most important issues that influence the validity of a COI study, and the ability to recognize the most common limitations in such work.